// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_URL_REQUEST_URL_REQUEST_THROTTLER_ENTRY_H_
#define NET_URL_REQUEST_URL_REQUEST_THROTTLER_ENTRY_H_

#include <stdint.h>

#include <queue>
#include <string>

#include "base/macros.h"
#include "base/time/time.h"
#include "net/base/backoff_entry.h"
#include "net/log/net_log.h"
#include "net/url_request/url_request_throttler_entry_interface.h"

namespace net {

class NetworkDelegate;
class URLRequestThrottlerManager;

// URLRequestThrottlerEntry represents an entry of URLRequestThrottlerManager.
// It analyzes requests of a specific URL over some period of time, in order to
// deduce the back-off time for every request.
// The back-off algorithm consists of two parts. Firstly, exponential back-off
// is used when receiving 5XX server errors or malformed response bodies.
// The exponential back-off rule is enforced by URLRequestHttpJob. Any
// request sent during the back-off period will be cancelled.
// Secondly, a sliding window is used to count recent requests to a given
// destination and provide guidance (to the application level only) on whether
// too many requests have been sent and when a good time to send the next one
// would be. This is never used to deny requests at the network level.
class NET_EXPORT URLRequestThrottlerEntry
    : public URLRequestThrottlerEntryInterface {
public:
    // Sliding window period.
    static const int kDefaultSlidingWindowPeriodMs;

    // Maximum number of requests allowed in sliding window period.
    static const int kDefaultMaxSendThreshold;

    // Number of initial errors to ignore before starting exponential back-off.
    static const int kDefaultNumErrorsToIgnore;

    // Initial delay for exponential back-off.
    static const int kDefaultInitialDelayMs;

    // Factor by which the waiting time will be multiplied.
    static const double kDefaultMultiplyFactor;

    // Fuzzing percentage. ex: 10% will spread requests randomly
    // between 90%-100% of the calculated time.
    static const double kDefaultJitterFactor;

    // Maximum amount of time we are willing to delay our request.
    static const int kDefaultMaximumBackoffMs;

    // Time after which the entry is considered outdated.
    static const int kDefaultEntryLifetimeMs;

    // The manager object's lifetime must enclose the lifetime of this object.
    URLRequestThrottlerEntry(URLRequestThrottlerManager* manager,
        const std::string& url_id);

    // The life span of instances created with this constructor is set to
    // infinite, and the number of initial errors to ignore is set to 0.
    // It is only used by unit tests.
    URLRequestThrottlerEntry(URLRequestThrottlerManager* manager,
        const std::string& url_id,
        int sliding_window_period_ms,
        int max_send_threshold,
        int initial_backoff_ms,
        double multiply_factor,
        double jitter_factor,
        int maximum_backoff_ms);

    // Used by the manager, returns true if the entry needs to be garbage
    // collected.
    bool IsEntryOutdated() const;

    // Causes this entry to never reject requests due to back-off.
    void DisableBackoffThrottling();

    // Causes this entry to NULL its manager pointer.
    void DetachManager();

    // Implementation of URLRequestThrottlerEntryInterface.
    bool ShouldRejectRequest(const URLRequest& request) const override;
    int64_t ReserveSendingTimeForNextRequest(
        const base::TimeTicks& earliest_time) override;
    base::TimeTicks GetExponentialBackoffReleaseTime() const override;
    void UpdateWithResponse(int status_code) override;
    void ReceivedContentWasMalformed(int response_code) override;

protected:
    ~URLRequestThrottlerEntry() override;

    void Initialize();

    // Returns true if the given response code is considered a success for
    // throttling purposes.
    bool IsConsideredSuccess(int response_code);

    // Equivalent to TimeTicks::Now(), virtual to be mockable for testing purpose.
    virtual base::TimeTicks ImplGetTimeNow() const;

    // Retrieves the back-off entry object we're using. Used to enable a
    // unit testing seam for dependency injection in tests.
    virtual const BackoffEntry* GetBackoffEntry() const;
    virtual BackoffEntry* GetBackoffEntry();

    // Returns true if |load_flags| contains a flag that indicates an
    // explicit request by the user to load the resource. We never
    // throttle requests with such load flags.
    static bool ExplicitUserRequest(const int load_flags);

    // Used by tests.
    base::TimeTicks sliding_window_release_time() const
    {
        return sliding_window_release_time_;
    }

    // Used by tests.
    void set_sliding_window_release_time(const base::TimeTicks& release_time)
    {
        sliding_window_release_time_ = release_time;
    }

    // Valid and immutable after construction time.
    BackoffEntry::Policy backoff_policy_;

private:
    // Timestamp calculated by the sliding window algorithm for when we advise
    // clients the next request should be made, at the earliest. Advisory only,
    // not used to deny requests.
    base::TimeTicks sliding_window_release_time_;

    // A list of the recent send events. We use them to decide whether there are
    // too many requests sent in sliding window.
    std::queue<base::TimeTicks> send_log_;

    const base::TimeDelta sliding_window_period_;
    const int max_send_threshold_;

    // True if DisableBackoffThrottling() has been called on this object.
    bool is_backoff_disabled_;

    // Access it through GetBackoffEntry() to allow a unit test seam.
    BackoffEntry backoff_entry_;

    // Weak back-reference to the manager object managing us.
    URLRequestThrottlerManager* manager_;

    // Canonicalized URL string that this entry is for; used for logging only.
    std::string url_id_;

    BoundNetLog net_log_;

    DISALLOW_COPY_AND_ASSIGN(URLRequestThrottlerEntry);
};

} // namespace net

#endif // NET_URL_REQUEST_URL_REQUEST_THROTTLER_ENTRY_H_
